1. Field of the Invention
The invention relates in general to a drive circuit of a thin-film transistor type liquid crystal display (TFTLCD), and more particularly, to a drive circuit that maintains a sufficient voltage to provide a normal operation of such drive circuit.
2. Description of the Related Art
Recently, the conventional widely used cathode ray tube (CRT) display has been gradually replaced by the flat panel display in small volume and light weight. Currently, the most popular flat panel display includes the liquid crystal display. The application of the liquid crystal display includes the low power products such as calculator, cellular phone, palm pilot, and the notebook computer, desktop computer, and even the wall television. To obtain an optimum display area of a liquid crystal display and to form a thinnest module, the technique of applying a drive integrated circuit (drive IC) has been intensively developed and studied.
There are two commonly used technique for applying the drive IC to the liquid crystal display. One is to connect a printed circuit board mounted with a drive IC to a liquid crystal panel, the other is to install a drive IC on a liquid crystal panel directly. The latter method is also called a chip on glass method (COG).
The former method has the disadvantages including the usage of expensive wiring board (normally polyamide), requirement of large amount of devices, and the need of additional equipment to complete the connection between the drive circuit and the liquid crystal panel. Moreover, when the terminal has a minute pitch, it further restricts the tape carrier pattern and the connection to the electrodes of the liquid crystal panel.
The chip on glass method is a technique for forming a compact display. The electrodes of pixels are formed on the thin-film transistor glass of the liquid crystal panel directly. The liquid crystal panel is patterned to install the drive circuit. The drive circuit is then connected to the liquid crystal panel. This method provides an improved yield and stability and the advantages of small volume and low cost.
However, in the conventional chip on glass structure, metal wires are used to the drivers. The resistance of the metal wires causes a significant voltage drop from one driver to the other. The voltage drop seriously affects the normal operation of the drivers. Therefore, a long strip flexible printed circuit board (FPC) is provided to directly connect each source driver. Therefore, the voltage drop caused by the connection via the metal wires can be obviated. This method requires a large area of the flexible printed circuit board. In addition, as the drive circuits include data lines and power lines, a multiple layer structure is required for the flexible printed circuit board. This method does not only increase the fabrication complexity of the flexible printed circuit board, but also increase the cost and the overall volume of the liquid crystal display. Moreover, as the fabrication process is more complex, the reliability is decreased.